The advantages of accurately and precisely measuring distance by energy reflection are self evident in that the need to physically traverse the distance with a tape or a counter is eliminated. The concept is to measure the time required for an incident of radiant energy to travel to and then from a target point. Based on this time of flight and the known speed of electromagnetic radiation, the distance from the measuring device to the target point can be calculated.
Development of techniques for precisely measuring shorter distances (e.g., <100 meters) with reflected laser has been technically challenging, however, because of the relative speed of electromagnetic radiation as compared to digital processing capabilities. More specifically, most available techniques struggle with the resolution of obtained results. Light travels in air at the speed of about 300 million meters per second. To measure distance with a resolution of one millimeter (mm), the radiant flight-time resolution would have to be in a range of 3 picoseconds (3×10−12 seconds).
Efforts at addressing this challenge for laser distance measurement are reflected in available patent documents. For example, U.S. Pat. No. 6,115,112 to Hertzman et al. describes using an initial measuring time interval longer than an estimated propagation time of the light signal to and from a target. U.S. Pat. No. 5,892,576 to Gaechter is directed to a method in which a special pulse pattern comprising echo signals for each of a series of pulses is used to determine the distance to an object producing the echoes.
Devices based on detecting phase changes between transmitted and reflected signals are represented by U.S. Pat. No. 5,949,531 to Ehbets et al. The '531 patent is directed to a device that calculates distance to a target based on the modulation phase shift of a beam of short pulses.
Although such laser-based range finders are known, this conventional technology offers equipment that is typically expensive and rather bulky. The market for such conventional devices is therefore somewhat limited. It would be desirable to provide methods and systems to accurately and precisely measure distance based on radiant energy reflection using relatively inexpensive components making possible a smaller, more cost-effective device.